1. Field of the Invention
The present invention relates to a small dielectric filter used for a high frequency radio appliance such as a portable telephone, etc., a dielectric filter which has strip line type resonator electrodes on a dielectric substrate, and connects them in electromagnetic field, a antenna duplexer, etc.
2. Related Art of the Invention
Recently, dielectric filters have been widely used as high frequency filters of portable telephones, etc., and have been requested to be smaller and thinner. Under the situation, a laminated dielectric filter which can be thinner than a coaxial type filter is expected to have a higher market share.
An example of the conventional laminated dielectric filter is described below by referring to the attached drawings.
FIG. 32 is an analytic oblique view of the structure of a conventional dielectric filter.
FIG. 33 shows an equivalent circuit of the dielectric filter shown in FIG. 32.
In FIG. 32, the dielectric filter is a structure including: dielectric layers 3401, 3402, 3403, 3404, and 3405; resonator electrodes 3406a and 3406b, transmission line electrodes 3407a, 2307b, and 3407c having input/output terminals on both ends; notch capacity electrodes 3408a and 3408b: and shield electrodes 3409 and 3410. These internal electrodes are formed between each dielectric layers.
As shown in FIG. 33, the dielectric filter forming the band rejection characteristic around the resonance frequency of the resonator includes resonators 3501a and 3501b, and transmission lines 3502a, 3502b, and 3502c connected through capacitors 3503a and 3503b. The capacitors 3503a and 3503b are respectively connected in series to the resonators 3501a and 3501b. Therefore, they functions as attenuation poles indicating high attenuation amounts around the resonance frequency of the resonators 3501a and 3501b. 
Normally, in the filter theory, the line length of the transmission line 3502c is set equal to xc2xc of the wavelength corresponding the resonance frequency of the resonators 3501a and 3501b so that a filter can be configured with the infinite impedance of the transmission line electrode 3502c, and the band rejection characteristic formed around the resonance frequency of the resonators 3501a and 3501b. 
FIG. 34 also shows an equivalent circuit of a filter forming a band rejection characteristic around the resonance frequency of a resonator. As shown in FIG. 34, the filter forming a band rejection characteristic around the resonance frequency of a resonator includes a transmission line having input/output terminals at both ends, a capacitor, and a resonator. A transmission line 4501 is connected to a resonator 4503 through a capacitor 4502.
Since the capacitor 4502 is serially connected to the resonator 4503, it functions as an attenuation pole indicating a high attenuation amount around the resonance frequency of the resonator 4503. In common filter designing, it is normal that input/output terminals at both ends have the same impedance values. Therefore, the values of elements forming a filter circuit are symmetrically designed.
However, to actually realize the configuration as shown in FIG. 32 as a dielectric filter, the long line of the transmission line electrode, which is a primary line of the filter, does not allow the transmission line having the length of xc2xc of the wavelength corresponding to the resonance frequency of the resonator to function as is on a dielectric layer which has a finite space. Therefore, wiring pattern of the transmission line can""t be formed straight, that is, the pattern becomes inevitably zigzag, and the width of the transmission line is reduced so that it can be designed on a dielectric layer or in a dielectric. The above mentioned configuration of a transmission line has the problem that it incurs the deterioration due to a loss in the pass band frequency of a dielectric filter forming the band rejection characteristic around the resonance frequency of the resonator.
With the configuration shown in FIG. 34, a filter forming a band rejection characteristic around the resonance frequency of a resonator can include attenuation poles equal in number to the resonators forming the filter. However, when the values of attenuation pole forming capacitors are equal, the positions of the plurality of attenuation poles are the same. Therefore, as shown in FIG. 36, there has been the problem that the rejection band is necessarily narrow. FIG. 35 is a Smith chart showing the state. Furthermore, when the above mentioned filter is used for one or both of the transmission filter and the reception filter of an antenna duplexer, the terminals connected at both ends of the transmission lines have different impedance values. Therefore, when the above mentioned filter is used for a antenna duplexer, there has been the problem that a filter characteristic has distortion, etc.
The present invention has been developed to solve the above mentioned problem, and aims at providing a small and thin laminated dielectric filter forming a band rejection characteristic around the resonance frequency of a resonator, and having a low loss characteristic at a desired frequency.
Furthermore, the present invention aims at realizing a filter having an excellent band rejection characteristic around the resonance frequency of a resonator with a simple configuration, and providing a filter having an excellent characteristic as a transmission filter and a reception filter of a antenna duplexer.
The 1st invention of the present invention is a dielectric filter, comprising:
a plurality of resonators; and
at least one transmission line provided among said plurality of resonators,
wherein a band rejection characteristic is formed around a resonance frequency of said resonator, and a line length of said transmission line is shorter than xc2xc of a wavelength corresponding to the resonance frequency of said resonator.
The 2nd invention of the present invention is the dielectric filter according to 1st invention, wherein said plurality of resonators are coupled in electromagnetic field.
The 3rd invention of the present invention is the dielectric filter according to 2nd invention, wherein:
a dielectric sheet and an electrode layer are layered and co-fired into one layered structure; and
said resonator and said transmission line are realized as an entire or a part of said electrode layer.
The 4th invention of the present invention is the dielectric filter according to 3rd invention, wherein
said dielectric sheet comprises at least one dielectric layer;
said electrode layer comprises:
a plurality of resonator electrodes provided on one primary surface of said dielectric layer; and
a transmission line electrode, provided on another primary surface of said dielectric layer, whose ends are input/output terminals;
said resonator electrode operates as said resonator; and
in a projection drawing where said resonator electrode and said transmission line electrode are viewing from a direction perpendicular to a surface of said dielectric layer, there are a plurality of overlapping portions of said transmission line electrode and adjacent said resonator electrodes, such portion of said transmission electrode that is positioned between each central point of said overlapping portions, corresponds to said transmission line, and a part of said transmission line electrode is positioned along central points of an overlapping portion of said resonator electrodes and said transmission line electrode, and corresponds to said transmission line.
The 5th invention of the present invention is the dielectric filter according to 3rd invention, wherein
said dielectric sheet comprises at least five dielectric layers from a first dielectric layer to a fifth dielectric layer;
said electrode layer comprises at least:
a first shield electrode, provided between said first dielectric layer and said second dielectric layer;
a plurality of resonator electrodes provided between said second dielectric layer and said third dielectric layer;
a transmission line electrode which has input/output terminals at both ends and is provided between said third dielectric layer and said fourth dielectric layer; and
a second shield electrode provided between said fourth dielectric layer and said fifth dielectric layer;
said resonator electrode operates as a resonator; and
in a projection drawing where said resonator electrode and said transmission line electrode are viewing from a direction perpendicular to a surface of said dielectric layer, there are a plurality of overlapping portions of said transmission line electrode and adjacent said resonator electrodes, such portion of said transmission electrode that is positioned between each central point of said overlapping portions, corresponds to said transmission line, and a part of said transmission line electrode is positioned along central points of an overlapping portion of said resonator electrodes and said transmission line electrode, and corresponds to said transmission line.
The 6th invention of the present invention is the dielectric filter according to 5th invention further comprising:
a plurality of adjusting electrodes provided on a surface of said fifth dielectric layer on which said second shield electrode is not provided; and
side electrodes which are provided on sides of said layered structure of said first to fifth dielectric layers and are connected to the input/output terminals on both ends of said transmission line electrode, wherein
said plurality of adjusting electrodes and said side electrodes are interconnected.
The 7th invention of the present invention is the dielectric filter according to 3rd invention, wherein
said dielectric sheet comprises at least five dielectric layers from a first dielectric layer to a fifth dielectric layer;
said electrode layer comprises at least:
a first shield electrode provided between said first dielectric layer and said second dielectric layer;
a plurality of first resonator electrodes provided between said second dielectric layer and said third dielectric layer;
a transmission line electrode which has input/output terminals at both ends and is provided between said third dielectric layer and said fourth dielectric layer;
a second shield electrode provided between said fourth dielectric layer and said fifth dielectric layer;
a second resonator electrode provided on a surface of said fifth dielectric layer on which said second shield electrode is not provided; and
a third resonator electrode which are provided on outer peripheral sides of said layered structure of said first to fifth dielectric layers and are connected to one end of said first resonator electrode and one end of said second resonator electrode;
said resonator electrode operates as a resonator; and
in a projection drawing where said resonator electrode and said transmission line electrode are viewing from a direction perpendicular to a surface of said dielectric layer, there are a plurality of overlapping portions of said transmission line electrode and adjacent said resonator electrodes, such portion of said transmission electrode that is positioned between each central point of said overlapping portions, corresponds to said transmission line, and a part of said transmission line electrode is positioned along central points of an overlapping portion of said resonator electrodes and said transmission line electrode, and corresponds to said transmission line.
The 8th invention of the present invention is the dielectric filter according to 3rd invention, wherein
said dielectric sheet comprises at least seven dielectric layers from a first dielectric layer to a seventh dielectric layer;
said electrode layer comprises at least:
a first shield electrode provided between said first dielectric layer and said second dielectric layer;
a plurality of first resonator electrodes provided between said second dielectric layer and said third dielectric layer;
a third shield electrode provided between said third dielectric layer and said fourth dielectric layer;
a second resonator electrode provided between said fourth dielectric layer and said fifth dielectric layer;
a transmission line electrode which has input/output terminals on both ends and provided between said fifth dielectric layer and said sixth dielectric layer;
a second shield electrode provided between said sixth dielectric layer and said seventh dielectric layer; and
a third resonator electrode which are provided on outer peripheral sides of said layered structure of said first to seventh dielectric layers and are connected to one end of said first resonator electrode and one end of said second resonator electrode;
said resonator electrode operates as a resonator; and
in a projection drawing where said resonator electrode and said transmission line electrode are viewing from a direction perpendicular to a surface of said dielectric layer, there are a plurality of overlapping portions of said transmission line electrode and adjacent said resonator electrodes, such portion of said transmission electrode that is positioned between each central point of said overlapping portions, corresponds to said transmission line, and a part of said transmission line electrode is positioned along central points of an overlapping portion of said resonator electrodes and said transmission line electrode, and corresponds to said transmission line.
The 9th invention of the present invention is the dielectric filter according to any one of 1st to 3rd inventions, wherein an open end of said resonator is a wide portion and a short circuit side is a narrow portion with a line width on the short circuit side made narrower halfway of said resonator.
The 10th invention of the present invention is the dielectric filter according to any one of 1st to 3rd inventions, wherein a central portion of said resonator is a wide portion, and a short circuit side and an open end side are narrow portions.
The 11th invention of the present invention is the dielectric filter according to any one of 1st to 3rd, 9th, and 10th inventios, wherein one end of said plurality of resonators is short circuited, and another end is set open.
The 12th invention of the present invention is the dielectric filter according to any one of 1st to 3rd, 9th, and 10th inventions, wherein both ends of said plurality of resonators are open or short circuited.
The 13th invention of the present invention is the dielectric filter according to any one of 5th, 7th, and 8th inventios, wherein all or a part of said first to third shield electrodes are connected and grounded.
The 14th invention of the present invention is the dielectric filter according to any one of 5th, 7th, and 8th incentions, wherein said first to fifth dielectric layers or said first to seventh dielectric layers have different thicknesses.
The 15th invention of the present invention is the dielectric filter according to any one of 5th, 7th, and 8th inventions, wherein said first to fifth dielectric layers or said first to seventh dielectric layers comprise dielectrics having relative dielectric constant.
The 16th invention of the present invention is a antenna duplexer, wherein a dielectric filter according to any one of 1st to 15th inventions is used as one or both of a transmission filter and a reception filter.
The 17th invention of the present invention is a communications appliance using a dielectric filter according to any one of 1st to 15th inventions.
The 18th invention of the present invention is the dielectric filter according to any one of 1st to 8th inventions used in microwave bands.
The 19th invention of the present invention is the dielectric filter according to any one of 1 to 8, wherein a line length of said transmission line is at least equal to or longer than {fraction (1/102)} of a wavelength corresponding to a resonance frequency of said resonator.
Normally, in the filter theory, the line length of a transmission line connecting resonators is xc2xc of the wavelength corresponding to the resonance frequency of a resonator to realize the band rejection characteristic at the resonance frequency of the resonator. However, according to the present invention, the line length of a transmission line connecting resonators can be shorter than xc2xc of the wavelength corresponding to the resonance frequency of a resonator to realize the band rejection characteristic at the resonance frequency of the resonator.
Since another dielectric filter according to the present invention can be free of becoming zigzag or wasteful wiring line using the above mentioned configuration, the present invention can provides a dielectric filter having a low loss characteristic at a pass band frequency.
In addition, with the above mentioned configuration, it is desired that a plurality of resonator electrodes and transmission line electrodes are provided in a dielectric.
Furthermore, with the above mentioned configuration, since filter components can bear ranged between upper and lower shield electrodes, a dielectric filter having a desired filter characteristic can be designed with no influence of an external electromagnetic field.
Furthermore, with the above mentioned configuration, a smaller dielectric filter can be realized using a dielectric sheet having a high specific inductive capacity. Additionally, a smaller communications appliance can also be realized.
With the above mentioned configuration, it is desired that a dielectric layer is layered below the first shield electrode and above the second shield electrode. With the configuration, the first and second shield electrodes can be protected.
Since another dielectric filter according to the present invention can form a resonator electrode by an external electrode with the above mentioned configuration, the filter characteristic can be adjusted in a trimming process using a luter, etc. Therefore, since the thickness and the specific inductive capacity of a dielectric sheet, and the inconstant electrode pattern can be absorbed, the yield in mass production can be improved.
In addition, since another dielectric filter according to the present invention can form an adjusting electrode using an external electrode with the above mentioned configuration, the adjustable frequency range can be extended by performing a trimming process using a luter, etc., thereby easily realizing an impedance matching dielectric filter. Furthermore, since the thickness and the specific inductive capacity of a dielectric sheet, and the inconstant electrode pattern can be absorbed, the yield in mass production can be improved.
Furthermore, since another dielectric filter according to the present invention can have a resonator electrode positioned not opposite a transmission line electrode with the above mentioned configuration, unnecessary electromagnetic field coupling between a resonator electrode and a transmission line electrode can be reduced, thereby successfully providing an easily designed dielectric filter.
Additionally, another dielectric filter according to the present invention has an open end of a resonator electrode as a wide portion, and a short circuit end as a narrow portion. With the structure, a resonance frequency can be lowered without along resonator electrode, there by providing a smaller dielectric filter.
Furthermore, another dielectric filter according to the present invention has the central portion of a resonator electrode as a wide portion, and a short circuit end and an open end as narrow portions. With the configuration, the deterioration by a conductor loss can be suppressed more effectively than a constant width of a resonator electrode, thereby successfully providing a dielectric filter having a low loss characteristic.
The 20th invention of the present invention is a dielectric filter comprising at least one transmission line, a plurality of resonators connected to said transmission line, and a plurality of capacitors provided between said resonator and said transmission line, and forming a band rejection characteristic around the resonance frequency of the resonator,
wherein a plurality of values of capacitances of said capacitors are different to each other.
The 21st invention of the present invention is the dielectric filter according to 20th inventions, wherein:
said transmission line has input/output terminals at both ends; and
said each capacitor of plurality of capacitors has different capacity values depending on impedance conditions at each input/output terminal of said transmission line.
The 22nd invention of the present invention is the dielectric filter according to 21st invention, wherein among said plurality of input/output terminals, capacity values of input/output terminals having higher impedance are smaller than capacity values of input/output terminals having lower impedance.
The 23rd invention of the present invention is the dielectric filter according to 20th invention, wherein said transmission line is formed by said resonator and said transmission line, which are plane electrodes, on a plurality of dielectric sheets as a layered structure co fired into laminated structure.
The 24th invention of the present invention is a dielectric filter having a layered structure, comprising:
a first shield electrode;
a dielectric layer (1) provided on said first shield electrode;
a plurality of resonator electrodes provided on said dielectric layer (1);
a dielectric layer (2) provided on said plurality of resonator electrodes;
a transmission line electrode which are provided on said dielectric layer (2) and whose both ends are input/output terminals;
a plurality of capacitors connected to said transmission line electrode, provided on same dielectric layer (2), positioned opposite said plurality of resonator electrodes partially through said dielectric layer (2);
a dielectric layer (3) provided on said transmission line electrode and said plurality of capacitor electrodes;
a second shield electrode provided on said dielectric layer (3); and
side electrodes provided on sides, wherein
a band rejection characteristic is formed around a resonance frequency of said resonator; and
an area of said resonator electrode opposite said capacitor electrode through said dielectric layer (2) is different each other from an area of said capacitor electrode.
The 25th invention of the present invention is the dielectric filter according to 24th invention, wherein open ends of said plurality of resonator electrodes are connected to other respective side electrodes.
The 26th invention of the present invention is the dielectric filter according to 25th invention, wherein a dielectric layer (4) is provided on said second shield electrode, adjusting electrodes equal in number to said resonator electrodes are provided on a top surface of said dielectric layer (4), and, among said plurality of side electrodes, said adjusting electrodes are connected to side electrodes connected to said resonator electrode respectively.
The 27th invention of the present invention is the dielectric filter according to 24th invention, wherein said side electrodes are connected to both input/output terminals of said transmission line electrode, a dielectric layer (4) is provided on said second shield electrode, an adjusting electrode is provided on a top surface of said dielectric layer (4), and said side electrodes connected to said transmission line electrode are connected to said adjusting electrodes respectively.
The 28th invention of the present invention is the dielectric filter according to 24th invention, wherein one end of each of said plurality of resonator electrodes is connected to a predetermined side electrode through a short circuit end, and another end of each of said plurality of resonator electrodes is an open end.
The 29th invention of the present invention is the dielectric filter according to 24th invention, wherein both ends of said plurality of resonator electrodes are open ends.
The 30th invention of the present invention is the dielectric filter according to 24th invention, wherein among said plurality of resonator electrodes, a thickness of at least one resonator electrode is different from thicknesses of other resonator electrodes.
The 31th invention of the present invention is the dielectric filter according to 24th invention, wherein
each of said dielectric layers has a dielectric material having a different specific inductive capacity.
The 32nd invention of the present invention is a antenna duplexer, comprising: a transmission filter and a reception filter,
wherein said transmission filter and/or said reception filter comprises the dielectric filter according to any one of 20th to 31st inventions.
The 33rd invention of the present invention is a communications appliance, comprising:
an antenna;
a matching circuit connected to said antenna:
a transmission filter connected to said matching circuit;
a transmission circuit connected to said transmission filter;
a reception filter connected to said matching circuit; and
a reception circuit connected to said reception filter,
wherein said transmission filter and/or said reception filter comprise the dielectric filter according to any one of 20th to 31st inventions.
The 34th invention of the present invention is a dielectric filter, comprising:
a plurality of resonators;
at least one transmission line provided among said plurality of resonators; and
a capacitor provided between said resonator and said transmission line,
wherein:
a band rejection characteristic is formed around a resonance frequency of said resonator;
a line length of said transmission line is shorter than xc2xc of a length of a waveform corresponding to a resonance frequency of said resonator; and
said plurality of capacitors have different capacity values.
The 35th invention of the present invention is the dielectric filter according to 34th inventions, wherein:
said plurality of resonators are coupled in electromagnetic field;
said transmission line has input/output terminals at both ends; and
each capacitor of said plurality of capacitors has different capacity values depending on impedance conditions at each input/output terminal of said transmission line.
The 36th invention of the present invention is the dielectric filter according to 35th invention, wherein among said plurality of input/output terminals, capacity values of input/output terminals having higher impedance are smaller than capacity values of input/output terminals having lower impedance.
The 37th invention of the present invention is the dielectric filter according to anyone of 34th to 36th inventions, wherein:
a dielectric sheet and an electrode layer are layered and co-fired into one layered structure; and
said resonator and said transmission line are realized as an entire or a part of said electrode layer.
The 38th invention of the present invention is a dielectric filter, comprising:
a plurality of resonators; and
at least one transmission line provided among said plurality of resonators,
wherein a band rejection characteristic is formed around a resonance frequency of said resonator, and a line length of said transmission line is longer than xc2xc of a wavelength corresponding to the resonance frequency of said resonator.
The 39th invention of the present invention is the dielectric filter according to 38th ivnention, wherein said plurality of resonators are coupled in electromagnetic field.
The 40th invention of the present invention is the dielectric filter according to 39th invention, wherein:
a dielectric sheet and an electrode layer are layered and co-fired into one layered structure; and
said resonator and said transmission line are realized as an entire or a part of said electrode layer.